BT Openreach UK Begins to Trial a Fix for G.INP Broadband Woes

After a small delay BTOpenreach has this week started to trial a fix for the latency and performance problems that were created on some superfast broadband Fibre-to-the-Cabinet (FTTC) lines following the recent introduction of Physical Retransmission ReTX (G.INP – ITU G.998.4) technology.

G.INP is an error correction solution that can help to tackle spikes / bursts of Electromagnetic Interference (impulse noise), which once enabled will make some problematic lines more stable and less prone to errors. Indeed it’s a good upgrade and one that should actually help to improve service performance and not lower it. Sky Broadband’s LLU lines already use it.

But problems started to surface in March, shortly after Openreach began their deployment, when some customers in related areas noticed a modest rise in the level of latency on their “fibre broadband” lines and many also experienced a loss of speed (here). Exactly the opposite of what should be happening.

At the time it was suggested that a big part of the problem related to the fact that not everybody was using a fully G.INP capable VDSL2 router or modem, which appeared to include some customers on Openreach’s own ECI modems (G.INP works on both upstream and downstream transmissions, but the ECI modem’s upstream doesn’t support it). We covered this in more detail during our late April update (here).

The good news is that Openreach have been developing a solution, which involves a change that would “remove the automatic application of interleaving in the upstream for those lines that do not need it. This will not impact the normal DLM processes, which may still apply retransmission / interleaving if the line requires it as was the case previously.”

A trial for this was intended to begin at the end of last month, but for reasons unknown it had to be delayed. Happily we can now confirm that Openreach have just begun the trial by loading the new DLM profiles to lines, which during the update will result in a loss of sync. At present the trial appears to be limited to pre-selected lines that are known to be suffering from the aforementioned problems, but if all goes well then it could soon be deployed elsewhere.

The deployment of G.INP is a useful precursor to the roll-out of Vectoring technology, which could give end-users in busy areas a big boost to FTTC broadband performance by tackling crosstalk interference. Vectoring is already live on over 100 DSLAMs (here) and a much bigger deployment is anticipated to follow.